| Aromatic polyimides (PIs) and aromatic polyamides (PAs) are two class of high-performance polymer materials because of their combination of thermal stability, electrical performance, flame retardancy and retention of physical properties at high temperatures. They have received considerable attentions in the aerospace, microelectronics, automobile and petrochemical industries. However, some applications of PIs and PAs are often limited by their poor solubility and high processing temperature mainly due to their rigid polymer backbones and the strong interchain interaction. Meanwhile, PIs often have strong absorption in the visible region and appear deep yellow colors, which may hinder their applications in the liquid-crystal display and optical waveguide.This paper mainly reports the synthesis of aromatic diamines and corresponding functional PIs and PAs. Based on the viewpoint of molecular design,4 series of PIs and PAs were prepared. Some special molecular structures and groups, such as the trifluoromethy group, the noncoplanar and the cyclohexane structure, were successfully introduced into the polymer chain. The obtained polymers all show improved solubility, excellent optical properties, high glass transition temperatures, and some of them also display low dielectric constant and water absorption. The main results include as follows.1. A high purity diamine monomer,3,3'5.5'-tetramethyl-4,4'-diaminodiphenyl-butyltoluene (BADP). was synthesize via one step from 2,6-dimethylaniline and benzaldehyde. The obtained diamine was subsequently employed to prepare a series of polyamides(PA-1～PA-3) with three aromatic dicarboxylic acids by means of the Yamazaki phosphorylation polycondensation technique. The inherent viscosity of the resulting polyamides were in range of 0.64～0.83 dL/g, and they exhibited an excellent solubility and optical property. They were readily soluble not only in some strong polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, but also had a good solubility in some low-boiling-point solvents such as chloroform. The maximum dissolvability of them even exceeded more than 10 wt% in these solvents. The polyamide film showed high optical transparency and colorless, with a UV-Vis absorption cutoff from 312 nm to 345 nm. Furthermore, the polyamide also showed good thermal and mechanical properties. The temperatures of 10% weight loss in air or nitrogen were higher than 380℃and 408℃respectively, and their glass-transition temperatures (Tg) were higher than 338℃. The polyamide films had strengths at break at 64～81 MPa, elongations to break of 8.0%～9.2%, and initial moduli at 1.4～2.0 GPa.2. The obtained diamine was subsequently employed to prepare a series of polyimides (PI-1～PI-4) with four commercial aromatic dianhydrides. The inherent viscosity of obtained PIs were in range of 0.57-0.84dL/g, and they exhibited an excellent solubility and optical property. They were readily soluble not only in some strong polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide,and N,N-dimethylformamide, but also had a good solubility in some low-boiling-point solvents such as chloroform, tetrahydrofuran, and dichloromethane.The maximum dissolvability of them even exceeded more than 10 wt% in these solvents. The polyimide films showed high optical transparency and colorless, with a UV-vis absorption cutoff from 341 nm to 365 nm. Furthermore, the polyimide also showed good thermal and mechanical properties. The temperatures of 10% weight loss in air or nitrogen were higher than 440℃and 500℃respectively, and their glass-transition temperatures (Tg) were higher than 333℃. The polyimide films had strengths at break at 62～95 MPa, elongations to break of 8.6%～15.5%. and initial moduli at 2.2～3.5 GPa.3. A series of novel polyimides (PI-1a, PI-1b and PI-2a, PI-2b) were polymerized from 4,4'-(cyclohexane-1,4-diylbis(oxy))bis(3-(trifluoromethyl)aniline) and 1,4-bis((4-amino-2-(trifluoromethyl)phenoxy)methyl)cyclohexane, with two aromatic tetracarboxylic dianhydrides using the typical one-step method. The inherent viscosity of these resulting PIs were in the range of 0.53-0.91 dL/g in N,N-dimethylacetamide at 30℃. They were readily soluble in numerous solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), meta-cresol (m-Cresol), and dimethylsulfoxide (DMSO). The PI films showed high optical transparency and were colorless with an ultraviolet-visible absorption cut-off wavelength around 330 nm, and a low dielectric constants of 2.49-2.93 at 1 MHz. The PIs also showed good thermal properties. Their glass-transition temperatures (Tg) were higher than 337℃, and the temperatures of 10% weight loss in air and nitrogen were higher than 412℃and 417℃. Furthermore, the PI films possessed good mechanical properties with tensile strengths of 54-71 MPa, elongations at break of 11.6-17.3% and low moisture absorption (< 1.34%). |
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